Ported vs. non-ported vacuum advance?
Thread Starter
Drifting
Joined: Apr 2005
Posts: 1,323
Likes: 3
From: I KNOW JESUS... HE'S MY GARDENER
Ported vs. non-ported vacuum advance?
I recall reading someone's post (Lars, most likely) discussing ported vs. non-ported vacuum for the vacuum advance. How do I identify the two? My carb is an Edlebrock replacement for the stock Q-Jet and has all the same ports as the Q-Jet plus a few extra.
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
well conventional wisdom says the one above the throttle butterflies is ported vacuum and the one below is direct vacuum....some times they are beside eadh other....easy way to tell is with a vacuum guage or i guess your finger....if it is "sucking" at idle it is direct manifold vacuum or non ported vacuum....if it has no "pull" at idle but does so when the car is at a higher RPM that is ported vacuum....
Thread Starter
Drifting
Joined: Apr 2005
Posts: 1,323
Likes: 3
From: I KNOW JESUS... HE'S MY GARDENER
And when should one or the other be used for vacuum advance? I'm having some "bogging" issues when I stomp on it. Gonna play around with timing, springs, etc. I'm going to re-locate the advance hose as an experiment...that won't cost anything.
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
you need to read Lars papers and his posts on this he makes it all logical whenhe says it and its correct....read the post XE268h that is going on now he talks about the vacuum cannisters and ported and direct vacuum there....
Le Mans Master
Joined: Mar 2004
Posts: 7,493
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From: Little Rock AR
Manifold vacuum needs the canister to be matched to your engine idle vacuum level while ported style is just hook it up and go.
Ported is better if you are not interested in "tuning it" yourself.
Manifold vacuum works better for cooling and stability at idle when tuned right. Manifold vacuum is what the factory used before emissions.
-Mark.
Ported is better if you are not interested in "tuning it" yourself.
Manifold vacuum works better for cooling and stability at idle when tuned right. Manifold vacuum is what the factory used before emissions.
-Mark.
